1. Technical Field
The field of art to which this invention pertains is that of a coextrusion apparatus, particularly for use in manufacturing annular seamless components of elastomeric materials such as used in the production of pneumatic tires, specifically body plies for radial tires. More particularly the invention relates to such a coextrusion apparatus in which the inner and/or outer profile of the tubular extrudate is varied by varying the amount of elastomeric material applied to the inner or outer surface of the extrudate.
2. Background Information
Tubular components or articles such as pneumatic tire body plies, have previously generally been built by utilizing woven fabric and calendering the same with rubber stock which, when cut to size, entails wrapping the sheet component around a tire building drum and overlapping the ends of the sheet to produce an annulus with a generally axially extending seam. In order to avoid this lapped or seamed construction, extrusion has been employed in the prior art whereby a tubular extrudate is produced containing reinforcement cords disposed therein.
Many of the problems with such lapped or seamed construction have been resolved by our previous invention of a coextrusion apparatus and method disclosed in U.S. Pat. Nos. 4,578,024 and 4,657,718, which are incorporated herein by reference in the interest of full disclosure. These earlier inventions provide a solution to the noted prior art problems by producing a generally tubular elastomeric ply or extrudate made up of first and second concentric tubular streams of elastomeric material having interposed adjacent their common interface, a closely and uniformly spaced array of parallel reinforcing elements. In the building of a tire, the carcass or first stage body consists of six elements namely, a body ply which is the reinforcing cord and skim, two sidewall bands or annuli, two body ply insert annuli and an inner liner. Heretofore assembly or placement of these six bands on a tire building drum required six separate manually performed steps wherein the individual strips were placed on the tire building drum.
These various individual strips of rubber usually were formed of different elastomeric compositions in order to achieve different results when assembled into the final tire. The inner liner is formed of a highly air impervious material and is applied to the body ply to provide the barrier for retaining the air within a tubeless pneumatic tire. The particular compound of the inner liner provides such impermeability characteristics. The present invention described below pertains particularly to the application of an inner liner on the tubular body ply component of a vehicle tire in forming a first stage tire wherein the body ply is extruded as a tubular extrudate and the inner liner applied at distinct locations on the inner surface of the tubular extrudate, in addition to applying an outer layer on the tubular extrudate, preferably of a different elastomeric material than the tubular extrudate.
The most pertinent prior art with respect to applying a layer of material on the inner surface of an extrudate are shown in the following patents.
U.S. Pat. No. 3,078,507 discloses an extruding device for making hollow cylinders and comprises an extrusion head having a central bore and an annular extrusion chamber. A control sleeve slides axially within a guide sleeve. This member can serve as a cutoff member or can be used to control the thickness of the extrudate flow. A control sleeve also is provided having an irregular beveled lower end so that thicker walls can be formed at opposite points of the extrusion.
U.S. Pat. No. 3,209,404 discloses a screw extruder having a barrel and a screw rotatable within the barrel. A die holder includes a die insert in a tubular mandrel. A rod is axially movable within a pin and a sleeve can be set to any desired position by controlling the pressure of the volume of fluid admitted to a cylinder in order to control the thickness of the wall of the tube being extruded. A valve actuating cam can be shaped to provide a desired cyclical fluid flow to the cylinder to obtain a predetermined variation in the wall thickness of the blank extruded from an orifice.
U.S. Pat. No. 3,281,896 discloses a parison extrusion die assembly having a movable mandrel, positioned within a cylindrical passageway in a die head. The longitudinal position of the mandrel can be adjusted so that the thickness of the tubular extrudate can be regulated by changes in the exit orifice.
U.S. Pat. No. 3,587,281 discloses an extrusion die having a mandrel head which is axially movable so as to vary the interior wall thickness of the tubular extrusion and completely stop the flow of extrusion material to terminate the extrusion. The extrusion apparatus includes a chamber, a die, and an axially movable mandrel with a tapering head defined by a lip. If the mandrel is driven in a predetermined direction, the extrusion material will not flow and the extrusion can be effectively cut to a predetermined length.
U.S. Pat. No. 3,944,641 discloses a device for altering the contour of the interior surface of a pipe wall. The apparatus comprises a rotatable blade or disc at the end of an extrusion mandrel. A lip formation is provided at the exterior surface of the mandrel outer end so as to form a plurality of grooves in the wall of the extrusion as the mandrel rotates. A linear actuator rotates the mandrel in the extrusion chamber.
U.S. Pat. No. 4,029,458 discloses an extrusion die having a linearly movable mandrel with a piston integrally formed along its intermediate portion which operates within a chamber. The thickness of the extrudate coming from a die is determined by the position of an annular edge of the mandrel with respect to the annular edge of a die head. When the control means alters the position of the piston the annular edge will be varied with respect to the annular edge of the die head to vary the shape of the parison being extruded.
U.S. Pat. No. 4,038,017 discloses an extrusion head, a die core, a sleeve and a movable annular piston. The piston is actuated by a hydraulic cylinder which raises and lowers a die core and adjusts the size of an annular opening which would alter the thickness of a laminate being produced by the extrusion head.
U.S. Pat. No. 4,047,868 discloses a parison extrusion molding machine comprising a special die head and a main extruder attached to the die head. The resin for the innermost layer of a composite is fed into an inlet from the main extruder. The thermoplastic resin flows through a passage which is defined by a sleeve wall and housing wall. The thickness of the laminate flow of the molten resin is controlled by adjusting the space between the inner sleeve of a pressure ring and the outer ring of a sleeve by moving an adjusting screw. Furthermore, the thickness of the parisons can be changed by varying the space between a core pin and die which results from vertical movement of a holder, together with the core pin.
U.S. Pat. No. 4,171,195 discloses a crosshead die in which the volume of the manifold can be varied so as to vary the relative wall thickness about the material flowing through the die. The apparatus includes a threaded collar, a forwardly extending sleeve and a frustroconical front portion which defines an orifice between the sleeve and rod. The wall thickness of material emerging from the orifice can be adjusted by axial movement of the rod and extension which changes the dimensions of the orifice.
U.S. Pat. No. 4,422,839 discloses an annular exit die for an extrusion head in which a die casing ring comprises generally concentric shells. The shells are nested within each other and are rigidly fastened to the housing of an extrusion head. A step portion is provided on one of the shells and the wall thickness of the extrudate can be varied at predetermined points as a result of the axial height adjustment of a die core. A lower edge of the die core forms the inner boundary of the die gap and displacement of the core downwardly in an axial fashion alters the wall thickness of the hollow extrudate.
U.S Pat. No. 4,465,449 discloses an extrusion feed block apparatus which comprises an extrusion die and a cylindrical torpedo element disposed within a central bore. Radial movement of the torpedo element by a spider body alters the dimensions of a passageway and, thus, the thickness of the inner layer of a pipe. This movement is accomplished by threading bolts inwardly and outwardly. A bushing also is radially adjustable for adjustment of the passageway. This device serves to control the thickness uniformity of an inner pipe layer and the overall uniformity of the laminate as it traverses the passageway.
U.S. Pat. No. 4,507,071 discloses an apparatus for forming a multiple layer laminated pipe. A die body is provided having a transitional body portion and a discharge sleeve at one end. The discharge sleeve is concentrically positioned within a sleeve adjustment body and includes an annular ridge engaged by an annular lip of a sleeve adjustment body. The sleeve is capable of slight radial movement. A plug can be used to reduce the flow of the central passage, and additional adjustments in the thickness of the outer layer and inner layer can be performed by rotating adjusting bolts so as to radially reposition the sleeve to a desired location.
U.S. Pat. No. 4,578,025 discloses a die assembly for extruding multi-layer parisons which includes a plurality of control rings for determining the thickness of each layer. The apparatus includes a core pin, a mandrel, and a plurality of control rings. Selection of the curvature and height of the control rings can be selected to change the thickness of the resin material passing through gaps formed therebetween. The overall thickness the combined resin laminate can be controlled by moving the core pin and die with a shaft prior to the resin exiting from the nozzle.
The most pertinent prior art with respect to applying and varying the outer profile of a tubular extrudate are shown in the following U.S. patents.
U.S. Pat. No. 3,134,832 discloses a method for extruding articles which comprises an extrusion die having a body and a cylindrical exterior sleeve. A central circular hole is provided and an elastomeric constrictive annulus which defines the extrusion aperture is positioned directly behind a flange. The annulus is held against the interior surface of the flange by a ring. As a gear is turned a follower is screwed into the exterior sleeve, pressing against the ring and annulus so that the annulus can expand inwardly under the compressive force in order to uniformly reduce the size of the hole in the annulus, i.e., reduce the size of the extrusion aperture.
U.S. Pat. No. 3,840,311 discloses an extrusion nozzle for manufacturing a plurality of frozen food type articles. This patent discloses an extrusion chamber having an inlet supply and terminating in an outlet orifice. A flexible wall formed from neoprene rubber can be attached to the casing wall adjacent the outlet in a conventional fashion. Five air cylinders are mounted on a frame which serve to indent a flexible wall so as to vary the shape of the wall and alter the dimensions of the exit orifice.
U.S. Pat. No. 3,940,221 discloses a die with a controllable lower lip opening. A metal die block is provided with a passageway for receiving flowable material which has a lower lip portion and an upper lip. The opening between the lips can be adjusted by moving an elongated metal rod having a head. The metal rod extends through a heater block, so that when the temperature is increased, the elongated rod increases in temperature and expands. A lower end of the heated rod will then be forcibly displaced in an axial direction, to press upon flexible lip and bend downwardly slightly to narrow the gap between the lips and decrease the thickness of the sheet which is being extruded.
U.S. Pat. No. 4,279,857 discloses a shaping nozzle having a core member surrounded by a two part sleeve to define an annular passageway which terminates in an exit passage around an outwardly and downwardly flared central pin or mandrel. An outer fixed ring surrounds an inner, elastic ring which has a substantially crescent shaped interior. A wedge engages an element and an outer ring, and movement of the wedge can determine the shape of the passageway at a given axial position. An axially displaceable piston defines the size of the passageway. An elastic ring having a cylindrical inner surface defines a part of flow passageway. Also, axial displacement of a piston causes movement of a frustoconical surface that defines a wall of the passageway and is capable of changing the thickness and shape of the passageway adjacent the nozzle.
U.S. Pat. No. 4,432,718 discloses an extrusion head comprising a die core and a casing ring located within a head housing. Each die ring section is axially adjustable by positioning screws so that the lower edge boundary of the die gap will be changed. In this fashion the extruded tube material will have walls of variable thickness at predetermined points and the thickness of the extruded tube will increase or decrease as a result of changes in the outer circumference of the tube while its interior contour remains the same.
Although certain of the prior art patents discussed above disclose an axially movable mandrel which is capable of either completely stopping or modulating the flow of material through an extrusion orifice, none of these patents disclose the specific configuration of applicant's apparatus as set forth below. In particular, the prior art does not disclose a relatively stationary cylindrical sleeve and a piston movable within the sleeve which has a rearwardly directed edge for modulating and/or cutting off the flow of extrudate, in combination with means for compensating for the pressure changes within the extrudate adjacent the orifice for applying the inner layer, to enable a precise cutoff and start of the inner layer as in our invention.
U.S. Pat. No. 4,776,909 which is assigned to the same assignee as the present application, discloses broadly a method for varying the thickness of an extrudate by varying the inner surface thereof by adjusting an extrusion die opening in a controlled manner so as to vary the feed rate of rubber to the extrusion orifice. However, no apparatus is shown or described in this earlier patent which compensates for the pressure exiting within the extrudate upon the stopping and starting of the flow of the extrudate when forming the inner layer to provide an accurate termination and start of the inner layer as in our invention.